24 
BULLETIN 6 2, HAWAII EXPERIMENT STATION 
around them, since humification is taking place outwardly and is 
working inwardly, gradually diminishing the size of the particles. 
That the foregoing considerations apply in considerable degree 
to organic Hawaii soils is indicated by the phenomenon that the 
adsorptivity of soils often approximates the adsorptivity of the 
colloids extracted therefrom and in some instances exceeds it. This 
will be shown later (p. 34), when the determination of the colloidal 
fraction by the water-vapor adsorption method is considered. 
To obtain an idea of the extent to which organic matter was pres- 
ent in the combined silt and sand fractions, the loss on ignition of 
this fraction was calculated for several soils from the loss on igni- 
tion of the whole soil, that of the extracted colloid, and from the 
mechanical analysis. Table 8 shows the comparison of loss on igni- 
tion of the colloidal and noncolloidal fractions in these soils. 
Table 8. — Comparison of loss on ignition of colloidal and noncolloidal fractions 
in Hawaii soils 
Soil No. 
Soil 
Colloids 
Noncolloids (sand 
and silt) 
Loss on 
ignition 
Amount 
Loss on 
ignition 
Amount 
Loss on 
ignition 
6. 
Per cent 
10.0 
30.0 
32.8 
16.3 
25.0 
13.0 
9.4 
9.6 
14.3 
18.9 
Per cent 
66.6 
27.0 
15.0 
49.3 
32.5 
30.1 
Per cent 
10.6 
19.7 
43.9 
17.5 
24.6 
15.3 
Per cent 
33.4 
73.0 
85.0 
50.7 
67.5 
69.9 
64.9 
69.4 
74.2 
71.9 
Per cent 
8.80 
9... 
33.81 
12 
30.84 
31. ... 
14.71 
42... . -.. 
25.19 
48. _. 
12.01 
65 
35. 1 9. 
9.62 
66... 
30.6 
25.8 
28.1 
8.6 
19. Q 
18.8 
10.04 
76 
12.67 
77 
18.94 
Table 8 shows that a considerable portion of the organic material 
is often obtained in the noncolloidal fraction. In most instances the 
loss on ignition of the noncolloidal fraction is close to that of the 
colloidal fraction and in some instances exceeds it. In the case of 
soil No. 9, a highly organic type, a much higher percentage of organic 
material is indicated in the noncolloidal fraction than in the colloidal. 
INORGANIC PHASE 
When the percentage of the organic matter is not the determining 
factor in soil-moisture properties, such as water-vapor adsorption, 
the texture of the soil partly determines that property. Structural 
character plays a role also, but under laboratory conditions this 
factor is eliminated. That the chemical composition of the inor- 
ganic phase plays a significant role has been indicated already where 
it was shown that two soils equally low in organic-matter content 
may have nearly the same percentage of clay fraction, and vet one 
soil may have more than three times as great a moisture equivalent 
as the other (see p. 22). Of course, this phenomenon may be noted 
not only in the case of moisture equivalents, but also with other 
moisture constants, such as hygroscopic moisture, or for that matter 
with other physical properties, such as heat of wetting and adsorp- 
tion of ions. That one may expect such behavior may be seen from 
the work of other investigators. 
